The present invention relates to a bridge assembly and, particularly, to a three-phase H-bridge assembly for a three-phase motor and a method of assembling the three-phase H-bridge assembly.
An inverter is a device or system that converts or changes a direct-current (DC) signal into an alternating-current (AC) signal. The inverter can be for a single-phase system or a polyphase system, such as a three-phase system. For a three-phase system, the inverter changes the DC signal into a three-phase AC signal. An exemplary use for a three-phase inverter is converting a twelve-volt DC signal generated by a battery (e.g., a vehicle battery) into a three-phase AC signal for powering a three-phase motor (e.g., a starting motor).
A rectifier is a device or system that changes an AC signal to a DC signal. The rectifier can also be for a single phase system or a polyphase system, such as a three-phase system. An exemplary use for a three-phase rectifier is converting a three-phase AC signal from a generator or electrical power station into a twelve-volt DC signal for charging a battery (e.g., a vehicle battery).
The invention provides a three-phase H-bridge assembly of an inverter/rectifier. The inverter/rectifier is used in connection with a three-phase motor/generator, and includes a controller that controls the three-phase H-bridge assembly. The three-phase H-bridge assembly includes a three-phase H-bridge circuit. The controller controls the H-bridge circuit resulting in either a DC signal being converted to a three-phase AC signal or a three-phase AC signal being converted to a DC signal.
For example, the inverter/rectifier may be used in connection with a vehicle. The inverter/rectifier may convert a twelve-volt DC signal from a vehicle battery into a three-phase AC signal, which is provided to a three-phase motor for starting the vehicle engine. In addition, the inverter/rectifier may receive a three-phase AC signal from the motor, which is acting as a generator, and convert the signal into a twelve-volt DC signal for charging the battery. Of course, the inverter/rectifier may be used only as an inverter or only as a rectifier. For the remainder of the application and for the claims, the term xe2x80x9cinverterxe2x80x9d implies an inverter, an inverter/rectifier, or even a rectifier.
The three-phase H-bridge assembly includes a first subassembly having a first terminal plate, a second subassembly having a second terminal plate, a third subassembly having a third terminal plate, and a fourth subassembly having a bus terminal plate. Each terminal plate includes a terminal acting as a connector capable of receiving a conductor. The first, second, and third terminal plates generate or receive one phase of the three-phase signal, and the bus terminal plate generates or receives one potential of the DC signal. Additionally, each terminal plate is electrically isolated from the other terminal plates.
The three-phase H-bridge assembly further includes first, second, third, fourth, fifth and sixth switching devices interconnected with at least one of the first, second, third and bus terminal plates. The first, second, third and bus terminal plates act as a heat sink for the switching devices connected thereto. In a preferred embodiment, the first switching device is interconnected with the first plate, the second switching device is interconnected with the second plate, the third switching device is interconnected with the third plate, and the fourth, fifth and sixth switching devices are interconnected with the bus terminal plate. However, in other embodiments, the switching devices may be interconnected with the plates differently (e.g., all six switching devices are mounted on the bus terminal plate).
The three-phase H-bridge assembly further includes a fifth subassembly having a bus board, and one or more fasteners. The subassemblies are retained in the three-phase H-bridge assembly by the one or more fasteners. In one embodiment, the bus board has a non-conductive material or surface on one side and a conductive material or surface on the other side. The conductive material acts as a ground plane and includes a terminal that generates or receives the second potential of the DC signal. For the preferred embodiment, the fastener interconnects the six switching devices with the bus board.
One feature of the invention has at least one of the first, second, third and bus terminal plates acting as a heat sink and, preferably, each of the first, second, third and bus terminal plates acting as a heat sink. That is, each switching device has a thermally conductive surface in thermal contact with a plate, and the plate acts as a heat sink for transferring thermal energy. Consequently, the plate has a dual purpose of acting as a terminal and as a heat sink. In addition, if the plate has too much thermal energy, a portion of the thermal energy may be transferred through the terminals and into the windings of the motor.
In one embodiment of the invention, the three-phase H-bridge assembly include seventh, eight, ninth, tenth, eleventh and twelfth switching devices. The first and seventh switching devices are electrically connected in parallel and are mounted on the first plate, the second and eighth switching devices are electrically connected in parallel and are mounted on the second plate, the third and ninth switching devices are electrically connected in parallel and are mounted on the third plate, the fourth and tenth switching devices are electrically connected in parallel and are mounted on the bus terminal plate, the fifth and eleventh switching devices are electrically connected in parallel and are mounted on the bus terminal plate, and the sixth and twelfth switching devices are electrically connected in parallel and are mounted on the bus terminal plate.
If the switching device are rated similarly and the multiple switching devices are connected in parallel, then the inverter circuit allows a greater current flow through the three-phase H-bridge assembly than if the three-phase H-bridge assembly did not include multiple switching devices connected in parallel. However, the increased current flow increases the amount of heat that needs to be removed. By mounting the switching devices on the terminal plates of the invention, the terminal plates can readily transfer the heat directly to the air, or transfer the heat into the windings of the motor.
The invention further provides a method of assembling a three-phase H-bridge assembly for a three-phase motor. The method includes forming first, second, third and fourth subassemblies. The first subassembly includes a first terminal plate, the second subassembly includes a second terminal plate, the third subassembly includes a third terminal plate, and the fourth subassembly includes a bus terminal plate. The forming step includes temporarily mounting the first, second, third and bus terminal plates to a mounting structure, mounting a first switching device to one of the first, second, third, and bus terminal plates, mounting a second switching device to one of the first, second, third, and bus terminal plates, mounting a third switching device to one of the first, second, third, and bus terminal plates, mounting a fourth switching device to one of the first, second, third, and bus terminal plates, mounting a fifth switching device to one of the first, second, third, and bus terminal plates, and mounting a sixth switching device to one of the first, second, third, and bus terminal plates. Preferably, the first switching device is mounted on the first plate, the second switching device is mounted on the second plate, the third switching device is mounted on the third plate, and the fourth, fifth and sixth switching device are mounted on the bus.
The method further includes interconnecting the first, second, third and fourth subassemblies with a fifth subassembly, and removing the first, second, third and fourth subassemblies from the mounting structure.
Other features and advantages of the invention will become apparent from the detailed description and accompanying drawings.